Right, so I have a python process which is running constantly, maybe even on Supervisor. What is the best way to achieve the following monitoring?
- Send an alert and restart if the process has crashed. I'd like to automatically receive a signal every time the process crashes and auto restart it.
- Send an alert and restart if the process has gone stale, i.e. hasn't crunched anything for say 1 minute.
- Restart on demand
I'd like the achieve all of the above through Python. I know Supervisord will do most of it, but I want to see if it can be done through Python itself.
I think what you are looking for is, Supervisor Events. http://supervisord.org/events.html
Also look at Superlance, its a package of plugin utilities for monitoring and controlling processes that run under supervisor.
[https://superlance.readthedocs.org/en/latest/]
You can configure stuff like Crash emails, Crash SMS, Memory consumption alerts, HTTP hooks etc.
Well, if you want a homegrown solution, this is what I could come up with.
Maintain the process state both actual and expected in redis. You can monitor it the way you want by making a web interface to check the actual state and change the expected state.
Run the python script in crontab to check for state and take appropriate action when required. Here I have checked for every 3 seconds and used SES to alert admins via email.
DISCLAIMER: The code has not been run or tested. I just wrote it now, so prone to errors.
open crontab file:
$crontab -e
Add this line at the end of it, to make the run_process.sh run every minute.
#Runs this process every 1 minute.
*/1 * * * * bash ~/path/to/run_monitor.sh
run_moniter.sh runs the python script. It runs in a for loop every 3 second.
This is done because crontab gives minimum time interval of 1 minute. We want to check for the process every 3 second, 20 times (3sec * 20 = 1 minute). So it will run for a minute before crontab runs it again.
run_monitor.sh
for count in {0..20}
do
cd '/path/to/check_status'
/usr/local/bin/python check_status.py "myprocessname" "python startcommand.py"
sleep 3 #check every 3 seconds.
done
Here I have assumed:
*state 0 = stop or stopped (expected vs. actual)
*state -1 = restart
*state 1 = run or running
You can add more states as per your convinience, stale process can also be a state.
I have used processname to kill or start or check processes, you can easily modify it to read specific PID files.
check_status.py
import sys
import redis
import subprocess
import sys
import boto.ses
def send_mail(recipients, message_subject, message_body):
"""
uses AWS SES to send mail.
"""
SENDER_MAIL = 'xxx@yyy.com'
AWS_KEY = 'xxxxxxxxxxxxxxxxxxx'
AWS_SECRET = 'xxxxxxxxxxxxxxxxxxx'
AWS_REGION = 'xx-xxxx-x'
mail_conn = boto.ses.connect_to_region(AWS_REGION,
aws_access_key_id=AWS_KEY,
aws_secret_access_key=AWS_SECRET
)
mail_conn.send_email(SENDER_MAIL, message_subject, message_body, recipient, format='html')
return True
class Shell(object):
'''
Convinient Wrapper over Subprocess.
'''
def __init__(self, command, raise_on_error=True):
self.command = command
self.output = None
self.error = None
self.return_code
def run(self):
try:
process = subprocess.Popen(self.command, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
self.return_code = process.wait()
self.output, self.error = process.communicate()
if self.return_code and self.raise_on_error:
print self.error
raise Exception("Error while executing %s::%s"%(self.command, self.error))
except subprocess.CalledProcessError:
print self.error
raise Exception("Error while executing %s::%s"%(self.command, self.error))
redis_client = redis.Redis('xxxredis_hostxxx')
def get_state(process_name, state_type): #state_type will be expected or actual.
state = redis.get('{process_name}_{state_type}_state'.format(process_name=process_name, state_type=state_type)) #value could be 0 or 1
return state
def set_state(process_name, state_type, state): #state_type will be expected or actual.
state = redis.set('{process_name}_{state_type}_state'.format(process_name=process_name, state_type=state_type), state)
return state
def get_stale_state(process_name):
state = redis.get('{process_name}_stale_state'.format(process_name=process_name)) #value could be 0 or 1
return state
def check_running_status(process_name):
command = "ps -ef|grep {process_name}|wc -l".format(process_name=process_name)
shell = Shell(command = command)
shell.run()
if shell.output=='0':
return False
return True
def start_process(start_command): #pass start_command with a '&' so the process starts in the background.
shell = Shell(command = command)
shell.run()
def stop_process(process_name):
command = "ps -ef| grep {process_name}| awk '{print $2}'".format(process_name=process_name)
shell = Shell(command = command, raise_on_error=False)
shell.run()
if not shell.output:
return
process_ids = shell.output.strip().split()
for process_id in process_ids:
command = 'kill {process_id}'.format(process_id=process_id)
shell = Shell(command=command, raise_on_error=False)
shel.run()
def check_process(process_name, start_command):
expected_state = get_state(process_name, 'expected')
if expected_state == 0: #stop
stop_process(process_name)
set_state(process_name, 'actual', 0)
else if expected_state == -1: #restart
stop_process(process_name)
set_state(process_name, 'actual', 0)
start_process(start_command)
set_state(process_name, 'actual', 1)
set_state(process_name, 'expected', 1) #set expected back to 1 so we dont keep on restarting.
elif expected_state == 1:
running = check_running_status(process_name)
if not running:
set_state(process_name, 'actual', 0)
send_mail(reciepients=["abc@admin.com", "xyz@admin.com"], message_subject="Alert", message_body="Your process is Down. Trying to restart")
start_process(start_command)
running = check_running_status(process_name)
if running:
send_mail(reciepients=["abc@admin.com", "xyz@admin.com"], message_subject="Alert", message_body="Your process is was restarted.")
set_state(process_name, 'actual', 1)
else:
send_mail(reciepients=["abc@admin.com", "xyz@admin.com"], message_subject="Alert", message_body="Your process is could not be restarted.")
if __name__ == '__main__':
args = sys.argv[1:]
process_name = args[0]
start_command = args[1]
check_process(process_name, start_command)
